Various methods have been proposed for limiting access to television signals to authorized customers who have made the proper arrangements for payment of the services. A common method is to encrypt the broadcast television signal and require the use of a security mechanism at the receiving end for decrypting or unscrambling the signal, provided the customer has a valid and current account with the service provider. Such a security mechanism may take the form of a set-top control box which is connected to the customer's television set and is activated by a special control code when access is authorized.
A new trend which appears to be emerging is to provide television receivers which are capable of simultaneously handling two or more different television programs. This enables the television set to provide a so-called “picture-in-picture” type display wherein two or more independent television programs are simultaneously displayed on the image screen in separate areas on the screen. The picture of lesser interest could be of smaller size occupying, for example, a corner portion of the image screen. Or one of the pictures could take the form of a program guide listing upcoming television shows.
Another reason for simultaneously receiving multiple television programs would be to record one program while watching another and different program.
Simultaneously handling two or more separate television programs complicates the providing of security mechanisms for controlling access to the programs. A logical solution would be to provide two or more separate security mechanisms, one for each television signal channel. This, however, would be an expensive solution. It would double or more than double the amount of security mechanism hardware needed. The present invention provides a better solution to the problem.